The operation of vehicles by persons under the influence of alcohol is a major safety problem in the United States and many other countries. Despite growing public awareness and government concern, statistics continue to show that a high percentage of automobile accidents causing serious injury or death involve drivers who have been drinking alcoholic beverages in excess. Injuries in the workplace are also often found to be related to the operation of heavy equipment or other machinery by persons impaired by the effects of alcohol.
To address this problem, various attempts have been made to develop devices intended to prevent automobiles and the like from being operated by inebriated individuals. Such devices, which are commonly referred to as "sobriety interlocks" are often based on the well known principle that the gas present in the alveoli of the lungs has an alcohol content directly proportional to that of the bloodstream. Blood alcohol content (BAC) thus can be accurately determined by breath testing A sobriety interlock is connected to the vehicle and normally operates to prevent the vehicle from being started unless one or more prerequisite conditions imposed by the interlock are satisfied. Foremost among such conditions is that any alcohol detected be present in a sufficiently low concentration although, the interlock may normally require any number of further conditions to be met before starting of the vehicle is enabled.
For example, it is generally acknowledged that to accurately determine BAC from a breath sample, an interlock must be designed to require delivery of a "deep lung" breath sample. As used herein and in the claims, that term refers to a breath sample consisting of a proportion of alveolar gas sufficient to permit an accurate determination of blood alcohol concentration. Since breath expired from upper portions of the respiratory tract does not necessarily have an alcohol level proportional to that of the bloodstream, a deep lung sample is essential if an interlock is not to be defeated by shallow exhalations of a series of short puffs of breath expelled from upper portions of the respiratory tract.
This problem is addressed effectively in U.S. Pat. Nos. 4,093,945 and 3,764,270 issued to Collier et al. The Collier et al. patents disclose means, such as a pressure switch and timer system, to ensure delivery of an essentially continuous and uninterrupted flow of breath sufficient to yield a deep lung sample. The sampling interval determined by the timer and the flow rate (as measured by the pressure sensor or other flow sensing means) are selected together to ensure a deep lung sample will be given. Unless breath is delivered at at least a minimum predetermined flow rate without interruption for the entire sampling interval, a required condition is not deemed satisfied and the vehicle cannot be started.
Unlike breath analyzer tests which are usually administered under the supervision of police or other trained persons, sobriety interlocks are routinely used outside the presence of persons other than the vehicle operator/test subject whose use of the interlock may be less than completely voluntary. One example of such a situation is where an employer seeks liability protection by installing interlocks on vehicles operated by employees. A higher degree of compulsion may be involved in some cases of court-supervised rehabilitation of offenders found to have been driving while under the influence of alcohol (DUI). As a mandatory condition for permitting a DUI offender to drive in order to maintain employment and/or obtain counselling, some courts may require a sobriety interlock to be installed in the offender's car. In such cases there is an increased likelihood that attempts to defeat the interlock will be made. Accordingly, the prior art has proposed various self-supervisory techniques directed toward avoiding circumvention of interlocks by various forms of subterfuge. These techniques typically share a common characteristic in that they require one or more additional conditions, usually unrelated to alcohol to be satisfied as prerequisites to starting the vehicle.
For example, techniques to discriminate between a contemporaneous breath sample and bogus gasses such air from a bicycle pump, filling station air hose or breath from a previously inflated balloon are discussed in U.S. Pat. Nos. 4,592,443; 3,831,707; and 3,824,537. Each of these patents proposes requiring one or more additional conditions be satisfied before permitting the vehicle to start. U.S. Pat. No. 4,592,443 requires the temperature of the gas delivered for a test to fall within a range expected for breath. Breath being moist, U.S. Pat. No. 3,831,707 requires the gas to contain appropriate humidity to avoid circumventing an interlock with a bogus gas that is drier than breath. U.S. Pat. No. 3,824,537 teaches requiring the operator to place one hand on a button which must be activated during a test period while the other hand is used to hold a breath sampling tube located some distance away from the button. Since both hands of the operator are placed apart, deceptive manipulation of a bellows or the like is discouraged. While all of these techniques have some merit, they are of little overall benefit if a sobriety interlock can be circumvented regardless of them by the simple artifice of enlisting the aid of a sober accomplice to take the test. This vexing problem is dealt with in U.S. Pat. No. 4,738,333 to Collier et al.
The technique proposed in the above '333 patent is to require the operator/test subject to identify himself or herself by correctly performing what is termed an "identity-confirming act" which the interlock is capable of recognizing. Unless this act is correctly performed within a limited number of attempts, the interlock will not permit the vehicle to be started regardless of the result of any alcohol breath test. Unlike a personal identification number (PIN) code which can be readily entered by another person who is merely given knowledge of the code, correct performance of the identity-confirming act requires a degree of skill which cannot ordinarily be acquired by most persons without attempting the act at least some minimum number of times. The limited number of attempts the interlock allows the act to be tried is selected to be lower than the minimum number of attempts ordinarily required to learn the act. In this way, the interlock can effectively discriminate between a trained designated person and a previously unskilled accomplice. Where a sobriety interlock includes such identification means, both the alcohol measuring phase and the identification phases of the test must be passed as prerequisites to enable starting of a vehicle or other equipment connected to the interlock.
One embodiment of the invention which is specifically described in the above-referenced '333 patent requires placing the mouth or lips over the breath sample delivery port of the system in order to deliver breath thereinto in a predefined manner to perform the identity-confirming act. By requiring use of the same physical location as that which is employed to deliver a breath sample for breath alcohol analysis to perform the identity-confirming act, increased assurance that these two acts will not be performed by different persons is provided. Further, the system can require either a very short time delay or no delay at all between breath sample delivery and the identity confirming act thus making it highly unlikely that two different persons could act quickly enough to deliver the breath sample and perform the identity confirming act. Even with such precautions it is desirable to even more positively ensure that the identity confirming act is performed by the same individual who delivers the breath sample.
Additionally, there are other forms of breath test apparatus in which users identity is determined from an act performed by the user by breathing or speaking into the mouthpiece of the breath tester, such as in the use of sobriety breath test apparatus employed with remote confinement or "home arrest" systems, such as are described in co-pending and commonly assigned U.S. patent application Ser. No. 4,843,377.
Accordingly, there exists a need to increase the assurance that a breath sample has not been delivered by artificial means or by one other than the identified operator of a sobriety interlock, particularly interlock systems of the type disclosed in U.S. Pat. No. 4,738,333.